NUCLEAR PLANT RESTART ASSAILED

Report finds partial restoration of power might increase risk

Restarting the San Onofre nuclear plant at reduced power would not resolve issues of rapid wear on steam generator tubes that have sidelined the plant for more than three months, and might make matters worse, says an analysis commissioned by an environmental group.

The report Tuesday by nuclear consultant and engineer Arnie Gundersen of Fairewinds Associates warns that reducing power would not provide a remedy for structural problems that are creating the vibrations among tubes in recently replaced steam generators at San Onofre. The analysis was commissioned by Friends of the Earth, an international organization that scrutinizes the nuclear-power industry.

More than 1,300 tubes — 3.4 percent of the total — have been plugged within San Onofre’s two reactors as plant operator Southern California Edison and federal nuclear safety regulators study the wear from tubes apparently rubbing against support structures and each other.

The generators were designed to operate efficiently with up to 8 percent of tubes plugged. But the rapid degradation of the high-pressure tubes carrying radioactive water through reactor cores — and a tube leak detected in January — continue to raise vexing safety issues.

An Edison executive has said the company may propose restarting the plant at lower power to dampen damaging vibrations.

“Fairewinds’ concern is that operating the San Onofre reactors at a lower power and flow rate might actually create a resonate frequency within the steam generators at which some tubes will vibrate as bad or worse,” the report said.

Gundersen, who said he was aided by other anonymous industry experts, also found that reduced power will not prevent previously damaged tube supports and plugged tubes from vibrating and damaging surrounding tubes and tube supports, and could worsen existing damage.

The Nuclear Regulatory Commission says there is no timetable for restarting the plant, which provides enough electricity to power about 1.4 million homes.

Edison indicated in a statement Tuesday that it still is studying generator inspection data as it attempts to fulfill federal safety requirements, as outlined in a “confirmatory action letter,” to return San Onofre to operation.

Much of the Fairewinds report also focuses on evidence that design changes to replacement steam generators, which were installed starting in 2009, warranted a more-thorough review by nuclear regulators. The concerns stem initially from a January trade magazine article on the redesign of generators at San Onofre, co-authored by two engineers, one with Edison and another working for generator manufacturer Mitsubishi Heavy Industries.

The report maintains that the more-thorough federal review of significant design changes was warranted and would have likely identified the problems before the steam generators were manufactured.

The NRC has said it was aware of the all proposed changes. Also on Tuesday, Sen. Barbara Boxer asked federal regulators for documentation about the review of generator design modifications at the plant.